FIELD OF THE INVENTION
The present invention relates to a zeolite-coatable metallic foil and to a process for producing a zeolite-coated foil.
Zeolites are specially composed and treated ceramic materials that have particular absorption properties for certain substances because of their composition and their structure. Typically, zeolites in a low temperature range can store large quantities of gaseous substances that they give up again at a higher temperature.
Concepts exist for utilizing those properties of zeolites, for instance in order to store hydrocarbons produced in the exhaust system of a motor vehicle in the cold-starting phase until a downstream catalytic converter is warm enough to convert those substances. After the exhaust system has heated up to a certain extent, the hydrocarbons are given up by the zeolite and are oxidized in the downstream catalytic converter, producing water and carbon dioxide.
In the case of such applications and similar ones, zeolites are applied especially as coatings to honeycomb bodies through which an exhaust gas can flow. Due to the ceramic composition of the zeolites, ceramic honeycomb bodies were first used as carriers for them. However, an attempt was also made to use metal honeycomb bodies, for instance of special steel, as carriers and to coat them with zeolite. However, under severe alternating thermal strains, such as occur in the exhaust systems of motor vehicles, for instance, high adhesion strength of the coating is important, and the different coefficients of expansion of metal and ceramic materials must be taken into account.